1. Field:
This disclosure is concerned generally with microbial growth media and specifically with media which include chemical growth indicators.
2. Prior Art:
Colonies of microorganisms grown on solidified or gel-like media are commonly located, examined, and counted using visible light which is transmitted through the media. This procedure becomes difficult under conditions in which the colonies are very small or transparent and in cases where the growth medium is opaque, highly colored, or very irregular. For example, if chocolate or milk agar is the growth medium, or if any medium is used on a wood or paper surface, it can be difficult to detect and study microbial colonies with transmitted light.
It is known that microorganism such as Pseudomonas fluorescens and Streptomyces fluorescens produce naturally fluorescent pigments and such microbes can be easily recognized by their fluorescence. It is also known that anionic or cationic fluorescent materials can be incorporated into growth media for the purpose of labeling individual bacteria. However, some of the anionic and cationic fluorescent materials have the disadvantages of being inhibitory to some microorganisms or they may react with particular components of some media.
The substance 8-anilino-1 -naphthalenesulfonic acid (ANS) has been used as a fluorescent probe in studying the interaction of a suspension of Escherichia coli and colicins. We are unaware, however, of the use of that material in a solidified, gel-like microbial growth media. Surprisingly, we have found that the incorporation of a small amount of ANS, or a salt thereof, into such media, makes possible the fluorimetric detection of microbial colonies. Hence, the problems associated with the use of transmitted light (e.g. opacity or translucency) are avoided. A detailed description of the growth medium is described below.